Design Simulation And Analysis Of Laterally Longitudinally Non Uniform Edge Emitting Gaas Based Diode Lasers Band 73

Design, simulation and analysis of laterally-longitudinally non-uniform edge-emitting GaAs-based diode lasers (Band 73)

Edge-emitting quantum-well diode lasers based on GaAs combine a high conversion efficiency, a wide range of emission wavelengths covering a span from 630 nm to 1180 nm, and the ability to achieve high output powers. The often used longitudinal-invariant Fabry-Pérot-type resonators are easy to design but often lead to functionality or performance limitations. In this work, the application of laterally-longitudinally non-uniform resonator configurations is explored as a way to reduce unwanted and performance-limiting effects. The investigations are carried out on existing and entirely newly developed laser designs using dedicated simulation tools. These include a sophisticated time-dependent laser simulator based on a traveling-wave model of the optical fields in the lateral-longitudinal plane and a Maxwell solver based on the eigenmode expansion method for the simulation of passive waveguides. Whenever possible, the simulation results are compared with experimental data. Based on this approach, three fundamentally different laser types are investigated: • Dual-wavelength lasers emitting two slightly detuned wavelengths around 784 nm out of a single aperture • Ridge-waveguide lasers with tapered waveguide and contact layouts that emit light of a wavelength of around 970 nm • Broad-area lasers with slightly tapered contact layouts emitting at 910 nm The results of this thesis underline the potential of lateral-longitudinal non-uniform laser designs to increase selected aspects of device performance, including beam quality, spectral stability, and output power.

Design, Simulation and Analysis of Laterally-longitudinally Non-uniform Edge-emitting GaAs-based Diode Lasers

Short channel GaN FET MMIC technology for high reliability applications (Band 74)

Nowdays GaN HEMT technology reached maturity level that allows industral fabrication of such devices for wide range of civil (telecommunications, power electrinics, automotive etc.), as well as space and military (phased array radars) applications. At this level, technology start reaching physical limits of GaN material and require new approaches that will allow to overcome some of well known problems related to GaN HEMTs, such as high gate leakage currents, reliability issues and difficulties of normally-off transistor fabrication. The goal of these theses is theoretical and experimental confirmation of the idea, that using peizoelectric nature of GaN crystal will allow local modification of GaN HEMT channel by means of external mechanical stress (using first and second passivation layers as stressors). After implementation of the proposed technology changes and new device geometry in process flow intended for 150 nm GaN HEMTMMIC fabrication, E/D devices with pinch-off voltages +0.1V and -1.65V respectively were fabricated on the same wafer within single process flow. It was observed, that E-mode devices, fabricated using compressed passivation layers, demonstrate lower gate leakage currents and more robust in HTRB test as compared to D-mode devices. In summary, it was demonstrated, that it is possible to control pinch-off voltage and gate leakage current of short channel GaN HEMTs by application of external stress. Usage of external stress, opens new degree of freedom in device optimization, and extends opportunities for more advanced MMIC design.